confused with if_baudrate

[Ben Hutchings]

On Thu, 2011-11-17 at 14:01 -0800, YongHyeon PYUN wrote:
> On Thu, Nov 17, 2011 at 01:39:24PM -0800, Juli Mallett wrote:
> > On Thu, Nov 17, 2011 at 13:12, Maksim Yevmenkin
> > <maksim.yevmenkin at gmail.com> wrote:
> > > hello,
> > >
> > > i'm a little bit confused about if_baudrate. from system headers
> > >
> > > #define if_baudrate ?? ?? if_data.ifi_baudrate
> > >
> > > and
> > >
> > > u_long ??ifi_baudrate; ?? ?? ?? ?? ?? /* linespeed */
> > >
> > > so, i'm taking this as if_baudrate really should be an interface line
> > > speed in megabits per second. am i correct? if so, then it appears
> > > that at least some drivers lie about true line speed. for example from
> > > ixgbe(4)
> > >
> > > ?? ?? ?? ??ifp->if_baudrate = 1000000000;
> > >
> > > it looks like its order of magnitude lower (i.e. 1 gigabit per second
> > > instead of 10 gigabits per second). am i missing something here or its
> > > just a typo?
> > 
> > ixgbe's developer is excessively concerned about overflow on 32-bit
> > hosts (and unwilling to correct it under a preprocessor conditional),
> > unlike several of the other 10GbE driver developers, although I think
> > one 10GbE driver opts to omit if_baudrate entirely.
> > 
> 
> Probably the driver could have used something like this.
> ifp->if_baudrate = IF_Gbps(10UL);
> 
> I think the driver should update if_baudrate depending on
> resolved speed(lost link, resolved speed etc).
> And if we really care about overflowing if_baudrate on 32bit
> machines, the IF_Gbps macro could be conditionally defined.

It could also overflow on 64-bit machines too because the caller didn't
know to use UL (which they shouldn't have to - what kind of
encapsulation is that?).  How about:

#define IF_Gbps(x) ((ulong)MIN(IF_Mbps((uint64_t)(x)), ULONG_MAX))

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
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